Diesel engines are amongst the largest emission sources in urban air. The emissions consist of soot particles of about 40-80 nm in diameter. The engines emit also nanoparticles at less than 20 nm or so in diameter, consisting of various hydrocarbons and possibly also sulphur (in case of sulphur containing fuel).
Why it is so attractive to switch to diesel instead of a less emitting gasoline engine? The answer is in fuel economy, which is one of the main advantages of using diesel engines. In Finland, the national policy towards diesel fleet has changed over the last couple of years. Today the price per liter is almost equal for both diesel and E10 gasoline. The owner of the diesel car needs to pay monthly tax, and the saving must come from the more economic engine.
The emissions of diesel engines are rather well know and there is continuous process to limit the emissions to even lower level. In 2013, the new EURO VI limits for heavy duty vehicles will be for PM (particulate matter) 0.01 g/kWh and for NOx 0.4 g/kWh. If you compare these to the EURO I values just 20 years ago the change is dramatic: EURO I for PM was 0.36 g/kWh and for NOx 8 g/kWh. Unfortunately, the diesel engines tend to be strong and last forever, so we have to wait for a while until the fleet has majority of EURO VI level engines.
In order to cut down the emissions to EURO VI level, the changes in engine technology will not be sufficient alone. This points out to the importance of the after treatment of the exhaust gases. Several different types of catalysts and filters exist. How well do these work? What is the efficiency of each one of them? These are the questions to be answered though intensive research work.
In order to make the development towards lower emissions even more challenging, one needs to consider also the effects of new type of fuels. As diesel fuel is possible to be made of e.g. biomass based renewable energy sources, there are activities to develop these alternative fuel types. These new generation of fuels aim for lower CO2 footprint.
Recent PhD work has focused on all of these in performing a wide set of experiments. I will examine the work on Friday 23rd November. The overall message is clear, one can fight against particle and gaseous emissions successfully together with lower greenhouse gas emissions.
The link for the press release of the thesis work can be found here in Finnish: